inhibit the normal spoilage microflora of the meat. Spices have also been
shown to stimulate the growth of lactic acid bacteria. This is a result of
their manganese content, spice extracts or spices low in manganese do
not have this stimulatory effect. Most aerobes have micromolar quanti-
ties of the enzyme superoxide dismutase (SOD) to scavenge the toxic
superoxide anion radical produced by a one-electron reduction of mo-
lecular oxygen (see Section 3.2.3). Aerotolerant lactic acid bacteria do
not have SOD but have developed an alternative protective mechanism
based on the accumulation of millimolar concentrations of manganous
(Mn^21 ) ion.
2HþþO 2 þMn^2 þ!H 2 O 2 þMn^3 þ ð 9 : 1 ÞThe Mn^21 is regenerated by a subsequent reduction step. Increasing the
manganese content of the medium can stimulate LAB growth.
Other ingredients which may be included are glucono-d-lactone which
improves acidulation by slowly hydrolysing to produce gluconic acid,
ascorbic acid to improve colour production and stability, and glucose to
supplement the available fermentable sugar in the starting mix.
Ingredients are blended together in a bowlchopper at low temperature.
When the ingredients have been blended together they are packed into
casings of the appropriate diameter. Traditionally collagen from the
gastrointestinal tract of animals has been used but nowadays fibrous
cellulose and regenerated collagen produced from animal hides are more
common. The packing material must have certain properties: it must
adhere to the meat mix and must shrink with it during processing and
must be permeable to moisture and smoke.
Fermented sausages are still often made by natural fermentations in
which the selectivity of the starting mix determines which components of
the heterogeneous microflora dominate. Starter cultures are however
being increasingly used for the greater assurance of a satisfactory
fermentation they provide. The principal components of commercial
starters are lactic acid bacteria and nitrate-reducing bacteria. Some will
also include yeasts and moulds such as Debaryomyces hanseniiand
Candida famata, and moulds, usuallyPenicilliumspp. such asP. nalgi-
ovense. LAB included in early starters were mainlyLactobacillus planta-
rum,Pediococcus acidilacticiandPed. pentosaceus, not necessarily those
most important in the natural fermentation. Surveys of naturally fer-
mented products demonstrated that the dominant LAB were psychrotro-
phic, facultatively heterofermentative lactobacilli (see page 317) that
were slightly less acid tolerant than usual (minimum pH 3.9 compared
with 3.7–3.8). Most of these are now assigned to the speciesLactobacillus
sakeandLactobacillus curvatusand strains of these have been incorpo-
rated into commercial starters.
344 Fermented and Microbial Foods